1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens which are suitable for use in a broadcasting television camera, a video camera, a digital still camera, a monitoring camera, and a silver-halide film camera, for example.
2. Description of the Related Art
In recent years, a zoom lens having a wider angle of view, a high zoom ratio, and high optical performance is required for an image pickup apparatus such as a television camera, a silver-halide film camera, a digital camera, or a video camera. As a zoom lens having a wider angle of view and a high zoom ratio, there is known a positive-lead type five-unit zoom lens constituted of five lens units including a lens unit having a positive refractive power disposed closest to the object side (see Japanese Patent Application Laid-Open Nos. H10-039216, 2010-191336, and H10-031157).
Japanese Patent Application Laid-Open Nos. H10-039216, 2010-191336, and H10-031157 each propose a zoom lens including a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having the positive refractive power, a fourth lens unit having the negative refractive power, and a fifth lens unit having the positive refractive power for imaging, in which the second, third, and fourth lens units move during zooming.
Japanese Patent Application Laid-Open No. H10-039216 discloses a five-unit zoom lens having a zoom ratio of approximately 5 and a photographing field angle of approximately 43 degrees at a wide angle end. Japanese Patent Application Laid-Open No. 2010-191336 discloses a five-unit zoom lens having a zoom ratio of approximately 3 and a photographing field angle of approximately 34 degrees at the wide angle end. Japanese Patent Application Laid-Open No. H10-031157 discloses a five-unit zoom lens having a zoom ratio of approximately 19 and a photographing field angle of approximately 76 degrees at the wide angle end.
In order to obtain high optical performance while maintaining a wider angle of view and a higher zoom ratio in the five-unit zoom lens, it is important to appropriately set a refractive power, a configuration, and the like of each lens unit. In particular, it is important to appropriately set movement conditions, the refractive power, and the like of each magnification varying lens unit. If these configurations are not appropriately set, it becomes difficult to provide a zoom lens having a wide angle of view, a high zoom ratio, and high optical performance over an entire zoom range.
In particular, the third lens unit having the positive refractive power has had a tendency toward an increase in lens diameter (effective diameter) when an attempt was made to attain a high zoom ratio of about 80 to 130. The increase in lens diameter of the third lens unit, which is a magnification varying lens unit, leads to increased variations in aberrations during zooming. In addition, when the lens diameter of the third lens unit is increased, a center thickness of each lens is generally increased in proportion to the lens diameter for securing an edge thickness and a strength thereof, which leads to a significant increase in weight of the entire third lens unit. As a result, a drive power for zooming is increased, which is disadvantageous in increasing the speed of a zooming operation and in improving operation followability in terms of mechanism, power consumption, and the like, and hence is undesirable.